I've been notified that the 'ftp.esri.com' server which has hosted 'se_toolkit' for the past... ohmygosh... 21 years will soon be retired. Since the 'C' API libraries are long-deprecated, and I haven't done any new development recently, I guess 'se_toolkit' will now be retired as well. Some of the functionality may come back as a Python package or three, but in the immortal words of Deforest Kelly, "He's dead, Jim."